Crystallinity in PPS–carbon composites: A study using diffuse reflection FT‐IR spectroscopy and differential scanning calorimetry

A method based on diffuse reflection Fourier transform infrared (FT‐IR) spectroscopy has been developed for determining the state of crystallinity in composite materials made from poly(phenylene sulfide) (PPS) reinforced with carbon fibers. Using this technique, good‐quality spectra can be obtained directly from the surface of prepreg or molded composite; thus the method is rapid and nondestructive. Several peaks in the spectrum are sensitive to the crystallinity and can be used for quantitative characterization purposes. The recommended indicator is the ratio of the heights of the peaks at 1075 and 1093 cm−1. Using a range of samples of varying crystallinity prepared by annealing amorphous prepreg, it has been shown that there is a very good correlation between this ratio and the enthalpy of crystallization as determined by differential scanning calorimetry. The effects of such annealing, as well as heating in air at high temperatures, have been investigated.